Ozonolysis

The ozonolysis, also Harries reaction is a reaction in the field of organic chemistry. The name is derived from the ozone used and the decisive reaction step: the destruction / dissolution (lysis ) of a carbon-carbon double bond. This method was discovered by Carl Dietrich Harries 1904 and 1905 published.

R is an organyl radical (for example alkyl ). Depending on the workup of the alkene products as carbonyl compounds ( aldehydes, in particular ), alcohols or carboxylic acids. By analyzing the products conclusions about the structure of the starting material are possible. Without modern methods such as NMR spectroscopy - - structure elucidation operated in this way was used to.

Other oxidation methods for working double bonds with osmium tetroxide, potassium permanganate or chromium compounds. In contrast to these methods, not only the pi-bonded, but additionally also the sigma - bond is broken during the ozonolysis.

Reaction conditions and mechanism

This reaction works especially well at low temperatures. Commonly used solvents are methanol, ethyl acetate and dichloromethane.

Mechanistically, the polar ozone is added via a 1,3-dipolar cycloaddition to the alkene in the first step. This forms the so-called primary ozonide (also called Molozonid ). This decays by rupture of the CC bond and one of the two O-O bonds in ozone ( cycloreversion ) to a carbonyl compound and a carbonyl oxide, which is highly unstable and occurs only as an intermediate. This form again by 1,3- dipolar cycloaddition of the so-called Sekundärozonid.

Through different workup of ozonolysis different products can be obtained: by simple hydrolysis of the Sekundärozonids form primarily the two carbonyl compounds. Since so but at the same time, hydrogen peroxide is formed, it can oxidize the products may continue.

Under certain conditions, it is not in the ozonation to form Primärozoniden but of epoxides, especially when bulky substituents are present at the double bond. These epoxides may rearrange to form aldehydes that result by further oxidation to carboxylic acids with an unchanged carbon skeleton.

Preparative can be worked either under oxidative or reductive conditions. Also, the receipt of the oxidation state of the two primary products is also possible. A reductive work would take place, for example, the addition of sodium borohydride - by the addition of triphenylphosphine protect the primary products from further oxidation. As ketones, carboxylic acids, esters, aldehydes, alcohols and acetals can be obtained depending on the selected processing.

An alkene [R = organyl radical (e.g., alkyl group )] ( 1 ) reacts with ozone to form a Molozinids (2). This is divided into a carbonyl compound ( 4) and a carbonyl oxide (3). These form below cycloaddition Sekundärozonid (5). Under reducing conditions produces two ketones ( 6).